The specification of Danish Pat. No. 99,616 discloses a hinge device intended for use in tilting windows and comprising two hinge parts adapted to be secured to the frame and the sash, respectively, of the window and including base plates with guide means thereon forming a part-circular guide channel and a corresponding slide member, respectively, defining a tilting axis spaced from the plane of the window. The present invention relates to such a hinge device which is particularly intended for windows to be mounted in an inclined roof and in which, as also applies to the practical embodiments of the hinge devices according to the patent referred to, the concave side of the part-circular guide channel is formed by a plate element, which is spaced from and by means of rivets or similar pins, is secured to the base plate of the hinge part, an arched blade spring being arranged in the spacing between the plate element and the base plate and having curved end portions gripping partly around and held in place by two of the rivets so that when the sash is moving close to its closed position, the concave surface of the blade spring frictionally engages a guide pin belonging to the hinge part with the slide member.
Such a blade spring is inexpensive to manufacture and may be mounted very easily and, generally, functions as intended when it is appropriately dimensioned for the size of the window and appropriately designed, to wit so that when unaffected the mid portion of the spring protrudes slightly from the concave side of the guide channel and has to be pressed backwards by the guide pin sliding therealong. Then the braking effect will to a substantial degree be due to the friction between the concave surface of the blade spring and the moving guide pin, and the conditions should be so that within an appropriately wide angular sector the friction is sufficient to hold the window sash in any desired ventilation position. Thus, the moment of the braking force around the tilting axis should be greater than the sum of the moments with respect to the same axis, of the gravity of the window sash and possible wind pressure thereon but, on the other hand, the braking force should not be great enough to impede the manual opening and closing of the window.
When calculating the dimensions of the spring it may be difficult to pay sufficient regard to these circumstances and, at the same time, to provide for the easy mounting of the blade spring on its carrying rivets as well as its firm connection therewith. In regard to its mounting, the spring should not be too rigid against bending but, at the same time, the braking effect of a too weak spring will be insufficient for the purpose.